1. Field of the Invention
This invention relates to devices generally used for the continuous separation and recovery of solids and/or liquid contained in slurries, especially those for recovering sugar crystals and molasses from so-called sugar massecuites.
2. Prior Art
So-called centrifugals have long been used and are still being used for separating commercial sugar crystals from molasses. However, this technique has many disadvantages in that, in order to develop the required centrifugal force, the so-called baskets, on which the screens are mounted, rotate at relatively high speeds (usually from 1000 to 1800 rpm), while the power required varies from 50 to 100 hp, thereby necessitating careful dynamic balance of the rotating parts and a sturdy construction of the system.
Furthermore, most of those centrifugals do not operate continuously (those who do have not been, so far, commercially successful, due to sugar crystal breakage and defective separation) in that they have to be stopped for admitting the massecuite and, again, when discharging the sugar crystals, thereby constituting a loss of time.
Recently, however, experiments were carried out with the prototype of a new system adapted for the continuous recovery of commercial sugar crystals and molasses. An application for patent is known to have been originally filed, in France, for protecting the system which, essentially, consists of a filtering belt supported on another perforated belt mounted on pulleys and a casing under vacuum. During operation, the massecuite is fed continuously on top of the filtering belt, while the molasses are recovered into the casing by the suction action of the vacuum and the remaining sugar crystals eventually scraped off and removed from the belt. The molasses are transferred from the casing to a degasifying chamber, before being removed from the system by means of a pump, whereas the sugar crystals (which apparently contain a relatively high percentage of moisture) are sent to a dryer. Reportedly, many problems were encountered during those experiments and which were mainly due to the difficulty in maintaining the required vacuum within the casing, because of the air which was constantly being sucked therein through "cracks" in the sugar layer. The formation of those "cracks" would, apparently, be the result of the inability for a belt to run truly level under such conditions.